Among the oil level detection devices for internal combustion engines in practical use today are ones where a float is provided within a housing, oil is introduced into the housing, and an excessive fall of an oil level is indicated to a user or the like when the float has lowered to a predetermined position.
For practical purposes, the conventional oil level detection devices for internal combustion engines have been considered satisfactory if they are constructed to allow the float to be unsusceptible to transitory oil level fluctuations. Examples of such oil level detection devices for internal combustion engines include one that employs a combination of a float and reed switch, as known, for example, from Japanese Utility Model Laid-Open Publication No. SHO-56-56143 (JP-UM-56-056143A).
FIG. 12 hereof is a sectional view explanatory of a fundamental construction of the conventionally-known oil level detection device 200 for an internal combustion engine, which includes: a housing 201 opening downwardly; a shaft 203 extending downward from a ceiling 202 of the housing 201; a float 204 slidably mounted on the shaft 203 and vertically movable (i.e., capable of rising and falling) in accordance with a level of oil 209 in the housing 201; a magnet 205 provided on the float 204; a reed switch 206 built in the shaft 203 to operate in response the magnet 205 approaching the switch 206; and bushes 208 attached to side surfaces 207 of the housing 201 for opening the side surfaces 207.
However, the conventionally-known oil level detection device 200 for an internal combustion engine would present the inconvenience that the float 204 sticks to the ceiling 202 or bottom 211 of the housing 201, due to the viscosity of the oil, preventing the oil level from being determined accurately. Further, in cases where the oil level detection device 200 is applied to a construction or civil engineering machine, such as a rammer or plate compactor, that vibrates greatly during operation, there would arise a possibility of some component parts, such as a reed switch 206, being impaired or damaged by fluctuating movement of the float 204. Such fluctuating movement of the float 204 would also wear the float 204, excessively fluctuate the oil level to be detected and make the float 204 stick to the housing more easily, leading to in false operation of the oil level detection device 200.
Thus, there has been a great demand for an improved oil level detection device for an internal combustion engine which can prevent the float from sticking to the ceiling or bottom of the housing due to the viscosity of the oil and prevent excessive stress from being applied to various component parts due to vibration transmitted from a machine (such as a civil engineering machine producing great vibration) equipped with the internal combustion engine.